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Some comments from a long time reader, infrequent poster. Many thanks to Fudman for his writeup and email advice (he also thanks Aioros, Cn90, Lbert, and others), Bluebee for her work compiling all the disparate info out there and Jason5Driver.

I've been leaking oil at widely varying rates. I finally decided it was time to do something about, and am starting with the CCV (thanks also to dansr for the in-person advice that finally got me going).

This is on an '03 530i M54.

Observation (many recycled, hopefully some new):
1. Label all connectors and where they plug in (I had a tough time finding the second OFH connection point at the end). I used masking tape and marker.
2. It was a pain removing the rubber vent hose on top of the upper intake boot. I ended up using a flat screwdriver on each side, wedged under the vent hose lip to pull it up and that worked well once applied.
3. The third nut on the wiring harness/box is more easily accessible/viewable with the plug to the throttle body removed.
4. I was able to reuse both intake boots without any trouble. Just be sure to loosen (or over loosen) the hose clamps. A 6mm GearWrench did the trick on the lower boot's connection to the throttle body.
5. It is possible to attach the connecting line (curvy one) to the CCV without removing the CCV, but it was not easy and I suspect removing the OFH would help.
6. Also on the connecting line, I confirm other reports that it can be pressed on CCV instead of rotated on. This is what I did, and could find no way to attach with rotating method in limited space. However, there is one orientation where the tab on the CCV will block the line from connecting with a click, so you'd just push forever without knowing. Practice connections in air first and note (maybe mark) needed alignment.
7. I don't know if throttle body gasket orientation matters. It doesn't appear to and other have testified any orientation works. (pic below)
8. I keep on breaking those dang plastic screw covers on the engine covers! Need to buy a bag full...
9. To repeat others, it's much easier to break the connector parts of the old hoses to remove. (see pic for example)
10. I also had no vacuum hose, just a rubber stopper. (see first pic of broken old CCV, rubber stopper pointing towards 1:00 position)

Questions:
1. I noticed a fair amount of mayo in the vent pipe. It's been somewhat cold here in VA and my typical work commute is 15-20 mins, so I hope it's the winter oil condensate vs something worse. This is my first winter with this car, but I noticed that on the prior E39, had oil tested and it was fine. Thoughts? (pics below)
2. There was also a good deal of mayo in the CCV (pics below), but none that I could find in the drain to the dipstick. Do you think this mayo is cold weather oil condensate or symptomatic of a "bad/failed" CCV that I've now replaced?
3. What is the proper oil level sensor behavior in terms of warnings? It never seemed consistent so I ended up just manually checking a few times a week.

I will now monitor oil level to see if it's stabilized.

Thanks again to all for the forum's wisdom. It helped a lot, but this all took about 8 hours over two days. Mostly in the dark, with a headlamp (with dying batteries), in my townhome's parking spot. Trying to get the car ready for the arrival of our first little one.